Ramon Aparece | What Evapotranspiration Data Actually Does for Irrigation Scheduling

Ramon Aparece on the greens


How replacing guesswork with a daily water-loss calculation changes what an irrigation system needs to run

The Number Behind the Schedule

Irrigation scheduling on most residential properties in Cape Coral is based on a schedule that was set at installation and adjusted occasionally based on how the lawn looks. Ramon Aparece uses a different starting point: evapotranspiration, usually abbreviated ET, which measures how much water the soil and plant surfaces are losing on a given day based on actual weather conditions. The ET value provides a replacement target rather than a guess.

What ET Measures and Where It Comes From

Evapotranspiration combines two processes: evaporation of water from the soil surface and transpiration of water through plant tissue. Together they represent the total water loss from a managed landscape on a given day. ET is calculated from weather data including temperature, solar radiation, wind speed, and relative humidity. The University of Florida's FAWN network (Florida Automated Weather Network) maintains weather stations across the state, including several in southwest Florida, that publish daily ET values.

On a hot, sunny, windy day in August, ET rates in southwest Florida can exceed 0.25 inches. On a cool, overcast, humid January day with no wind, the rate drops to under 0.05 inches. Scheduling a system that delivers 0.25 inches per session across three irrigation days per week in January is overwatering by a factor of several times. Delivering the same amount in August is accurate. A fixed schedule has no mechanism for knowing the difference.

How to Apply ET Data to a Schedule

The practical application of ET data to a schedule involves two steps. The first is converting ET values into irrigation run times based on the system's delivery rate. If a zone delivers 0.5 inches of water per hour of operation, then covering a daily ET of 0.2 inches requires about 24 minutes of run time spread across the permitted irrigation days.

The second step is accounting for rainfall. Rain that falls in the 24-hour period before a scheduled irrigation reduces or eliminates the need for that session. A functioning rain sensor handles part of this by shutting off the system after recent rainfall. Smart controllers that connect to local weather stations calculate both ET and recent rainfall automatically and adjust daily schedules without manual intervention.

Aparece installs and programs these controllers on properties where efficiency is a priority. The upfront cost is typically offset within a single growing season in water savings for most properties in southwest Florida, where water costs and the cost of overwatering-related disease treatment both factor into the calculation.

What Changes When You Schedule This Way

The most immediate change is that the system runs less in the wet season and more in the dry season, which is the opposite of what most fixed schedules produce. Fixed schedules typically get set in the dry season when the system is most needed, and then those same settings run through the wet season when the grass does not need supplemental irrigation on most days. ET-based scheduling adjusts automatically as conditions shift.

The second change is that the schedule responds to weather events individually rather than waiting for a season-level adjustment. A week of overcast weather in March reduces the ET calculation and reduces the irrigation need automatically. A dry, hot stretch in October, outside the normal wet season but above the dry-season baseline, triggers additional irrigation before the grass shows stress rather than after.

For southwest Florida properties with mature plant material and established turf, the difference in plant health between a fixed schedule and an ET-based schedule is most visible in the transitions between seasons. The ET-based schedule tracks the lawn's actual need rather than approximating it.

A Practical Starting Point Without a Smart Controller

Not every property needs a smart controller to improve on a fixed schedule. Aparece recommends a middle approach for properties where a full smart controller is not the immediate goal: pull the weekly ET average for each month from the FAWN network, calculate the corresponding run times for each zone based on delivery rate, and set a different seasonal schedule for each of southwest Florida's two main seasons, adjusting in November and again in April.

This is not as precise as a daily ET-based adjustment, but it is substantially more accurate than a year-round fixed schedule. The information is publicly available, and the calculation requires measuring the output of each zone with catch cans, which is a useful test to run regardless of the scheduling method being used.


Ramon Aparece on the greens

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